British research showing that sperm counts have dropped by almost a third in a decade has prompted renewed concerns about male fertility.
A study of 7,500 men, who attended the Aberdeen Fertility Centre between 1989 and 2002, showed that average sperm concentrations fell by nearly 30 per cent.
Lead researcher Dr Siladitya Bhattacharya said this was a cause for concern and the reasons behind it needed to be explained.
Researchers conducting the SPIN (Semen Parameters in the Northeast) study analysed 16,000 semen samples from men attending the Aberdeen clinic - the only fertility clinic in the Grampian area of Scotland.
They found that the average sperm count of those men with a 'normal' concentration - defined as over 20 million sperm per millilitre - fell from 87 million/ml to 62 million/ml over 14 years - a drop of 29 per cent.
It is believed that in the past 50 years, sperm counts around the world have fallen by almost 50 per cent.
Drug use, alcohol, smoking and obesity are among the factors most frequently blamed for a decline in the number and quality of sperm. Environmental factors such as pesticides, chemicals and radioactive material have also been linked to decreases in fertility.
In 1986, Scotland was among the regions of the UK affected by the fallout from the Chernobyl disaster, after radioactive dust carried hundreds of miles by the clouds came down when it rained.
But Dr Bhattacharya said it was "almost impossible" to say whether this, or what among any of the other factors were definitively linked to declining sperm counts.